Lifting device for a conveyor system a conveyor system and a method

ABSTRACT

Lifting device ( 1 ) for a conveyer system, comprising a housing ( 2 ) and a lift head ( 14 ), where the lift head ( 14 ) is adapted to hold a pallet ( 5 ). The lifting device ( 1 ) comprises a linear actuator ( 10 ) attached to a lift ( 14 ), said linear actuator ( 109 ) is adapted to lift a pallet ( 5 ) from a first, low position at the conveyor track to a second, raised position that is substantially vertical above the first position. The application also refers to a conveyer system and a method for lifting objects.

TECHNICAL FIELD

The present invention relates to a lifting device for a conveyor system.

BACKGROUND ART

Conveying devices, such as those which are used for moving objectsbetween different stations in a factory, usually comprise a conveyingtrack in the form of a belt or a chain. The conveying tracks can berecessed in a trench with vertical side surfaces. Alternatively, theycan be located on the horizontal upper surfaces of the trench orarranged in some other way. The objects to be conveyed are arrangedslidably in relation to the conveying tracks, either directly or viatransportation means, which are also known as pallets.

A pallet is conveyed along the conveying device comprising differentwork stations. In some cases, every work station will perform oneoperation on the transported object. In those cases, the work flow isdesigned such that every pallet will stop at every work station. Inother cases, for example when different products or different versionsof the same product are produced in the same product flow, all palletsdo not have to stop at all the work stations.

If the conveying device is of a conventional type, in which all workstations are positioned after each other and the operations on theobjects are performed synchronous, every pallet have to stop at eachwork station. If no operation is to be performed on an object at aspecific work station, the object will have to wait at that work stationuntil the operation on the previous object at that work station isready, until the object can continue. All pallets are in this casereleased at the same time and moves at the same time. One advantage ofsuch a system is that it is easy to predict the performance of thesystem. One disadvantage of such a system is that it is not veryflexible. If the operation time at a work station is long, all objectswill have to wait that time, even if there is no operation performed onall objects or if the operation time at another work station isconsiderably shorter. Thus, such systems are mostly used for a singleproduct or when the differences in the products are small.

In other systems, the operations on the objects are performedasynchronous, i.e. the pallet stops at a work station where an operationis to be performed, and is released when the operation is ready. In suchsystems, a relatively large buffer is required between each work stationin order to compensate for the different through-flow times of theproducts and for the different operation times at a work station.

Another way of compensating for different operation times at a workstation is to use two or more work stations that perform the same task.They are often positioned close to each other, and the object is stoppedat the work station that is free. In this way, the through-flow time ofthe system can be balanced in order to avoid bottlenecks in the system.

Normally, the operator setting up the system will try to coordinate thework so that every pallet spends the same length of time at each workstation. Sometimes, it is difficult to coordinate the operation time ateach work station. One solution, apart from using a buffer, is to locatesome work stations along different sub-conveyors located on the side ofthe main conveyor. Such a solution will require extra space and extraparts, such as a drive motor and means to divert objects to thesub-conveyor. This solution will work in some cases, but in other cases,especially when the product flow is altered after production hasstarted, it may not be possible to rebuild the conveying system withsuch a solution. There is thus room for improvements.

DISCLOSURE OF INVENTION

An object of the invention is therefore to provide a lifting device fora conveyor system and a method for lifting objects at a conveyor system.

The solution to the problem according to the invention is described inthe characterizing part of claim 1. Claims 1 to 11 contain advantageousembodiments of the lifting device. Claim 12 contain an advantageousconveyor system. Claim 14 contain an advantageous method for liftingobjects at a conveyor system.

With a lifting device for a conveyor system, comprising a housing and alift head, where the lift head is adapted to hold a pallet, the objectof the invention is achieved in that the lifting device comprises alinear actuator attached to a lift head, where said linear actuator isadapted to lift a pallet from a first, low position at the conveyortrack to a second, raised position that is substantially vertical abovethe first position so that a second pallet can pass underneath theraised pallet.

By this first embodiment of the lifting device according to theinvention, a lifting device that can lift an object from a position at aconveyor track to a raised position above the first position isprovided. This is advantageous in that the object is moved from theregular flow of the conveyor system, allowing the regular flow tocontinue without disruption.

In an advantageous development of the invention, the lift head displaysa first, open state and a second, closed state. This allows the lifthead to hold a pallet when the pallet is to be raised, and at the sametime allows for an easy release of the pallet.

In an advantageous development of the invention, the lift head comprisesa spring shaft that opens the lift head when the spring shaft bears on ahold surface. The advantage of this is that the lift heads do notrequire separately powered opening and release means.

In another advantageous development of the invention, the spring shaftbears on the hold surface when the lifting device is in the first, lowposition. The advantage of this is that the lift head is opened at thesame time as the lift head reaches the low position. This means that thelift head will always be open when the lift head is in the low position.A closed lift head in the low position, obstructing the pallet flow, isthus avoided.

In an advantageous further development of the invention, the lift headis closed by a clamping spring. This is advantageous in that the lifthead will be closed when it is in any position but the low position.

In an advantageous further development of the invention, the lift headis opened by a separate opening means. This is advantageous in that itallows the lift head to be opened in the raised position.

In an advantageous further development of the invention, the liftingdevice comprises a compressed air cylinder for the movement of thepallet from the first to the second position. This is advantageous inthat compressed air is a clean and cheap power source.

In an advantageous further development of the invention, the lift headcomprises a locating pin adapted to interact with a locating bushing ina pallet. This is advantageous in that an increased safety and accuracycan be obtained. To further increase the accuracy, the lift head mayalso comprise a recess adapted to the shape of the pallet.

In an advantageous further development of the invention, the liftingdevice further comprises a second housing with a second linear actuatorbeing attached to a second lift head. This is advantageous in that theload capacity and the accuracy of the lifting device can be improved.

In a first embodiment of the conveyor system, the conveyor systemcomprises an inventive lifting device. In this way, a conveyor system inwhich work can be performed on one object at the same time as anotherobject passes underneath is obtained. This allows for an efficientconveyor system.

In an advantageous further development of the conveyor system, thesystem comprises a plurality of inventive lifting devices, where thelifting devices are positioned close to each other, and where onelifting device is used to raise and/or lower a pallet at the same timeas another lifting device holds a pallet in the raised position,allowing a work station to perform an operation on an object held bythat pallet. This is advantageous in that the efficiency of the conveyorsystem is improved further.

In a first embodiment of the method for lifting objects which areconveyed along a conveying track comprising a conveyor chain and guiderails, said objects being conveyed on pallets, the object of theinvention is achieved by the steps of stopping a first pallet at apredefined position at a first lifting device, fixating the pallet tothe lifting device by clamping the pallet between a support plate and aclamping plate, and raising the pallet from a first, low position to asecond, raised position with the lifting device. The advantage of thisis that a method of raising an object is obtained, in which the objectis moved out of the regular flow of the conveyor system in an easy andflexible way.

In an advantageous further development of the invention, the methodcomprises the step of holding a second pallet in the second, raisedposition with a second lifting device simultaneously as the first palletis raised with the first lifting device. The advantage of this is that apallet can be raised at the same time as work is performed on an objectheld by another pallet. The work station can thus be used in anefficient way.

In an advantageous further development of the invention, the methodcomprises the step of holding the first pallet in the second, raisedposition with the first lifting device simultaneously as the secondpallet is lowered with the second lifting device. The advantage of thisis that a pallet can be lowered at the same time as work is performed onan object held by another pallet. The work station can thus be used inan efficient way.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in greater detail in the following, withreference to the embodiments that are shown in the attached drawings, inwhich

FIG. 1 a shows a first embodiment of a lifting device according to theinvention,

FIG. 1 b shows the lifting device according to FIG. 1 a in a raisedposition,

FIG. 2 a shows a second embodiment of a lifting device according to theinvention,

FIG. 2 b shows the lifting device according to FIG. 2 b in a raisedposition,

FIG. 3 a shows the lift head of the lifting device in an open state, and

FIG. 3 b shows the lift head of the lifting device in a closed state.

MODES FOR CARRYING OUT THE INVENTION

The embodiments of the invention with further developments described inthe following are to be regarded only as examples and are in no way tolimit the scope of the protection provided by the patent claims.

FIGS. 1 a and 1 b show a first embodiment of a lifting device for aconveyor system according to the invention. The lifting device 1comprises a housing 2 attached to some kind of support structure, e.g.to a stand 6. A conveyor track 3 comprising a drive chain 7 and guiderails 4 is also attached to the support structure. The conveyor track isadapted to convey pallets 5 in a known manner. A conveyor track of thistype is well-known to the skilled person and is not described further.

The housing 2 of the lifting device is positioned on one side of theconveyor track. In one embodiment, the housing is attached to thesupport structure and the conveyor track is thereafter attached to thehousing. The attachment means for the conveyor track is in thisembodiment integrated with the housing. This is advantageous when thelifting device is part of the original system, i.e. is designed in thesystem. In another embodiment, the housing is attached to the supportstructure after the conveyor track is mounted. The housing is in thisembodiment free-standing and may be mounted to the support structure atany time. This is advantageous when the production flow is altered orwhen a new product or version is introduced to the product flow. In thisway, the conveyor track does not have to be rebuilt in order to mountthe lifting device.

The lifting device comprises a linear actuator 8 mounted in the housing.The linear actuator can be powered in various ways, e.g. by electricityor pressurised air, but also hydraulic linear actuators are possible touse. The power source is selected e.g. depending on the type of energysource available and the type of required control means. If the systemuses pressurised air, which is common in conveyor systems, it may be ofadvantage to use pressurised air also to power the linear actuator.

The linear actuator 8 comprises in this example two shafts, a firstshaft 11 and a second shaft 12. The purpose of the shafts is to supportand guide the lift head and to allow a smooth movement of the lift head.The shafts are supported in the housing in a low friction way, e.g. bysliding bearings, so that a smooth movement is achieved. Preferably,each shaft is supported by one bearing in the bottom region of thehousing and one bearing in the top region of the housing in order toobtain a truly linear movement. The shafts are attached at the top endsby a lift head. The shafts 11, 12 are attached to a lift head 14. Thenumber and shape of the shafts may be chosen in different ways, as longas a proper movement is obtained. Square or triangular shafts are e.g.plausible.

The linear actuator further comprises a drive piston 13, fixedlyattached to the clamping plate 16 of the lift head 14. The drive pistonwill move the head of the lifting device between a first, low positionand a second, raised position. The drive piston is in this example thepiston of a compressed air cylinder. The drive piston 13 may also be thethreaded screw of an electric driven linear actuator, or may be anysuitable drive means depending on the selected power source.

The lift head 14, shown in FIGS. 3 a and 3 b, comprises a support plate15 to which the shafts 11, 12 are rigidly fixated. A clamping plate 16is positioned somewhat below the support plate 15. The clamping plate isslidable guided by the shafts 11, 12, i.e. the shafts extend through twoholes in the clamping plate. The clamping plate and the support plateare connected to each other by a clamping spring 17 and a spring shaft18. The first end of the spring shaft 18 is fixated to the support plate15 and extends through a hole in the clamping plate 16. The spring shaftis provided with a head 19 at the second end. The clamping spring 17 ispositioned between the head 19 and the clamping plate 16. In this way,the clamping spring will force the support plate and the clamping platetowards each other with a force which depends on the selected spring.

The lift head 14 is provided with a protrusion in the form of a locatingpin 22 that fits in a locating bushing integrated in the pallet. It isalso possible to provide the clamping plate with a shape, e.g. a recessin the support plate and/or the clamping plate that is adapted to theshape of the pallet that is to be lifted. By such an adaptation, thepallet will be held securely in place and a slight misalignment of thepallet during the stopping of the pallet can be compensated for.

The lifting device can be in either of two positions, a first, lowposition as seen in FIG. 1 a and a second, raised position as seen inFIG. 1 b. In the first, low position, the lift head of the liftingdevice is at the same level as the conveyor track. In this position, thelift head is open and allows a pallet to pass the lifting device withoutinterference. In the second, raised position, the head is closed inorder to hold a pallet in a raised position. Thus, in this position, thesupport plate and the clamping plate are forced together by the clampingspring, i.e. the head is closed. In the raised position, an operation onthe object transported by the pallet can be performed by a work station.It is also possible to use the raised position as a means to let anotherobject pass the raised object.

When the lift head of the lifting device is in the first, low position,the head will be open. FIG. 3 a shows the lift head 14 in an open stateand FIG. 3 b shows the lift head 14 in a closed state where the head israised. In the open state, the head 19 of the spring shaft 18 will bearon a hold surface 20 in the lifting device. To reach the opened state,i.e. to place the lifting device in the first, low position, anappropriate signal is sent to the lifting device. The drive piston willretract into the cylinder, pulling the lift head 14 down towards the lowposition. The head 19 of the spring shaft 18 will reach the hold surface20 and will stop there, bearing on the surface. At the same time, thesupport plate will stop at its lowest position, since the support plateis fastened to the spring shaft. The drive piston will continue pullingthe clamping plate further down, compressing the clamping spring 17.When the drive piston is completely retracted, the clamping plate hasreached its lowest position. The support plate and the clamping plateare as far apart as possible and the head 14 is opened.

When a pallet has stopped at the lifting device and a lift signal issent to the lifting device, the drive piston will extend out of thecylinder. This will move the clamping plate upwards, towards the lowerside of the pallet. When the clamping plate reaches the pallet, thepallet will be lifted slightly so that it bears on the support plate.The support plate is kept at its lowest position by the clamping springuntil the pallet reaches the support plate. When the drive pistoncontinues to extend out of the cylinder, the pallet will be held betweenthe support plate and the clamping plate. The support plate will thus bepushed upwards only when the pallet is securely held by the lift head.When the pallet is held firmly between the support plate and theclamping plate by the clamping spring, the pallet will be raised by thedrive piston towards the raised position.

When the lifting device is in the low position, pallets can pass thelifting device without having to stop at the lifting device. This ispossible because the head of the lifting device is opened and neither ofthe support plate nor the clamping plate extends into the path of thepallet. Since the closing action of the lifting device is integratedwith the lifting action, an erroneous closing of the lifting device atits low position is avoided. Thus, a closed lift head obstructing theflow of the conveyor system is avoided.

If a pallet is to be raised to the raised position, the pallet isstopped at the lifting device. The pallet is stopped at the liftingdevice either by stopping the conveyor chain or by using a special stopmechanism at the stop position. The type of stop used is determined bythe type of system used and the required accuracy. The lifting devicewill then lift the pallet to the raised position as described above. Inthe raised position, a work station can be positioned, in which sometype of action can be performed on the goods transported by the pallet.By mounting a lifting device according to the invention to an existingconveyor system, a flexible way to retroactively add a work station to aconveyor system is obtained. The added work station does not hinder theregular work flow of the conveyor system. Further, it allows otherpallets to pass the work station when an operation is performed at thework station. If the goods on the pallet are not required to stop at thework station, the pallet can just pass the work station without havingto stop at all.

When the pallet has been in the raised position, the lifting device islowered when the lifting device receives a lowering signal. The deviceis lowered by, in this case, the drive piston retracting into thecylinder. When the head of the spring shaft touches the hold surface,the support plate and the clamping plate starts to part, letting thepallet loose. When the low position is reached, the pallet is free tocontinue to move along the conveyor track.

The clamping action of the lift head can also be achieved in other ways.It is possible to use an active locking head, driven by e.g. pressurisedair and controlled separately from the lifting action. Such a clampingaction has the advantage that the pallet can be released also in theraised position, should there be a need. A disadvantage is that theenergy for the locking head must be available at the head of the liftingdevice and not only at the housing of the lifting device. Such asolution will also require more control lines.

In a second embodiment of the inventive lifting device, shown in FIGS. 2a and 2 b, the lifting device comprises a first housing 2 and a secondhousing 9. The first housing 2 is described above. The second housing 9is in this embodiment more or less identical to the first housing 2. Itis of course possible to design the second housing in a different mannerin order to adapt the lifting device to specific requirements. Bydesigning the housing 2 with linear actuator 8 and lift head 14 in asymmetrical manner, it is possible to use the housing on both sides ofthe conveyor track, acting as both the first and the second housing. Thesecond housing comprises a second linear actuator 10, similar oridentical to the linear actuator 10 described above. The second actuatoris mounted to a second lift head 21 being similar or identical to thefirst lift head 14.

Both the first housing and the second housing are mounted to the supportstructure of the conveyor system, e.g. to a stand 6, in the same way asdescribed above. The first housing is in this example mounted on theright side of the conveyor track, as seen in the travelling direction ofthe conveyor chain, and the second housing is in this example mounted onthe left side of the conveyor track.

When an object is to be raised by the lifting device, a signal is sentto the two linear actuators 8, 10 by the control system of the conveyorsystem. The two linear actuators will simultaneously raise the palletwith the object to the raised position. At the same time, the two liftheads 14, 21 will simultaneously clamp the pallet between the supportplate and the clamping plate of the lift heads, thereby holding thepallet in a firm grip. One advantage of using two linear actuators andtwo lift heads to raise a pallet is that the load capacity of thelifting device is increased. Another advantage is that the accuracy isincreased. This is especially advantageous when an operation that putsstress on the pallet is performed on an object, e.g. drilling ormounting of parts.

In a further embodiment of the inventive lifting device, the linearactuators of both sides of the lifting device, i.e. linear actuators 8and 10, are driven by one power source. In one example, the two linearactuators are powered by one compressed air cylinder, and the drivepiston of the pressurised air cylinder is connected to both linearactuators. This can be done e.g. by placing the pressurised air cylinderat the stand of the conveyor system. In this way, it is secured thatboth sides of the lifting device will lift simultaneously.

In a further embodiment of the inventive lifting device, the liftingdevice comprises a plurality of housings with a linear actuator and alift head, positioned side by side at the conveyor track. This isadvantageous when e.g. a robot or the like performs an operation on theraised object. By using two or more lifting devices positioned side byside, one lifting device can raise an object to the work station at thesame time as an operation is performed on an object held by anotherlifting device. Depending on the operation time, one of the liftingdevices or a third lifting device can be used to lower an alreadyprocessed object when work is performed on a raised object. In this way,the work station can be used in an efficient way.

The invention is not to be regarded as being limited to the embodimentsdescribed above, a number of additional variants and modifications beingpossible within the scope of the subsequent patent claims.

REFERENCE SIGNS

-   1: Lifting device-   2: Housing-   3: Conveyor track-   4: Guide rail-   5: Pallet-   6: Stand-   7: Drive chain-   8: Linear actuator-   9: Second housing-   10: Second linear actuator-   11: First shaft-   12: Second shaft-   13: Drive piston-   14: Lift head-   15: Support plate-   16: Clamping plate-   17: Clamping spring-   18: Spring shaft-   19: Spring shaft head-   20: Hold surface-   21: Second lift head-   22: Locating pin

1-17. (canceled)
 18. A lifting device for a conveyer system, comprising:a housing and a lift head, where the lift head is adapted to hold apallet, where the lifting device is adapted to be mounted on one side ofan endless drive chain without interrupting the drive chain, wherein thelifting device comprises a linear actuator attached to a lift head,where the lift head is adapted to grip the pallet from one side, wheresaid linear actuator is adapted to lift a pallet from a first, lowposition at the conveyor track to a second, raised position that issubstantially vertical above the first position so that a second palletcan pass underneath the raised pallet.
 19. The lifting device accordingto claim 18, wherein the lift head displays a first, open state and asecond, closed state.
 20. The lifting device according to claim 19,wherein the lift head comprises a spring shaft that opens the lift headwhen the spring shaft bears on a hold surface.
 21. The lifting deviceaccording to claim 20, wherein the spring shaft bears on the holdsurface when the lifting device is in the first, low position.
 22. Thelifting device according to claim 18, wherein the lift head is closed bya clamping spring.
 23. The lifting device according to claim 18, whereinthe lift head is opened and closed by a separate opening means.
 24. Thelifting device according to claim 23, wherein the opening means is acompressed air cylinder.
 25. The lifting device according to claim 18,wherein the lifting device comprises a compressed air cylinder for themovement of the pallet from the first to the second position.
 26. Thelifting device according to claim 18, wherein the lift head comprises alocating pin adapted to interact with a locating bushing in the palletto be held.
 27. The lifting device according to claim 18, wherein thelift head comprises a recess adapted to the shape of the pallet to beheld.
 28. The lifting device according to claim 18, wherein the devicefurther comprises a second housing with a second linear actuator beingattached to a second lift head.
 29. A system comprising: a conveyorsystem including a lifting device including a housing and a lift head,where the lift head is adapted to hold a pallet, where the liftingdevice is adapted to be mounted on one side of an endless drive chainwithout interrupting the drive chain, wherein the lifting devicecomprises a linear actuator attached to a lift head, where the lift headis adapted to grip the pallet from one side, where said linear actuatoris adapted to lift a pallet from a first, low position at the conveyortrack to a second, raised position that is substantially vertical abovethe first position so that a second pallet can pass underneath theraised pallet.
 30. The system according to claim 29, wherein the systemcomprises a plurality of lifting devices, where the lifting devices arepositioned close to each other, and where one of the plurality oflifting devices is used to raise and lower a pallet at the same time asanother one of the plurality of lifting device holds a pallet in theraised position, allowing a work station to perform an operation on anobject held by the pallet.
 31. A method for lifting objects which areconveyed along a conveying track comprising an endless conveyor chainand guide rails, the lifting objects being conveyed on pallets, themethod comprising: stopping a first pallet at a predefined position at afirst lifting device; fixating the pallet to the lifting device byclamping the pallet between a support plate and a clamping plate; andraising the pallet from a first, low position to a second, raisedposition with the lifting device.
 32. The method according to claim 31,including: moving the pallet from the first, low position to the second,raised position using a linear actuator.
 33. The method according toclaim 31, wherein the method further comprises: holding a second palletin the second, raised position with a second lifting devicesimultaneously as the first pallet is raised with the first liftingdevice.
 34. The method according to claim 33, wherein the method furthercomprises: holding the first pallet in the second, raised position withthe first lifting device simultaneously as the second pallet is loweredwith the second lifting device.